The goal of this application is to measure the effects of hyperosmotic fluid environment on vocal fold mucosal physiology and vocal function. Previous research has suggested that the isosmotic fluid environment of the vocal folds is necessary for regulating vocal fold mucosal physiology and ease of voice production. However, the isosmotic fluid environment of the vocal folds is easily perturbed by everyday exposure to poorly conditioned inhaled air, smoke, and pollutants. These perturbations raise the concentration of salts, proteins, and particulate in the effects of hyperosmotic vocal fold surface fluid on vocal function and mucosal physiology surface fluid, creating a hyperosmotic environment. Data from other biological tissues indicate that a hyperosmotic surface environment is detrimental to tissue physiology, but, the effects of hyperosmotic vocal fold surface fluid (VFSF) on vocal fold mucosal physiology and vocal function are not known. This application will utilize a combination of native tissue protocols and human subject experiments to (1) Measure the effects of hyperosmotic surface fluid on vocal fold mucosal ion transport, and production of inflammatory mediators (2) Characterize the chemical composition of hyperosmotic VFSF in healthy subjects and speakers reporting vocal fatigue, who are completing an oral breathing challenge at low humidity (3) Examine whether the physiological effects of hyperosmotic VFSF induced by oral breathing at low humidity are evident in clinical measures of Phonation Threshold Pressure and (4) Demonstrate reversal of the effects of hyperosmotic VFSF induced during oral breathing, by humidifying inhaled air. These translational experiments will address the relevance of studying the effects of hyperosmotic surface fluid on vocal fold mucosal physiology by demonstrating that hyperosmotic VFSF persists in speakers with vocal fatigue. Further, this application will offer novel empirical evidence for the beneficial effects of humidifying ambient air in restoring the local fluid environment of the vocal folds. Improved understanding of the chemical composition of VFSF, and the role of VFSF in regulating mucosal physiology, are paramount to developing scientifically-grounded hydration treatments, and personalized pharmacological strategies for individuals with voice problems. Hyperosmotic vocal fold surface fluid results from everyday challenges to the local vocal fold environment. This application will demonstrate that hyperosmotic vocal fold surface fluid adversely affects mucosal physiology and is a proinflammatory stress, but that these detrimental effects can be prevented by to examine the interdependencies among the dependent variables. Given the enormous economic and societal costs associated with treating voice problems, the focus on prevention is both timely and relevant.